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4 


32X 


7hH 


I:) 


[Fr*»m  thb  AMERICA^f  Journal  of  Sciknce,  Vol.  I,  March,  1896.1 


ON    A    NEW    ALKALI    HORNBLENDE    AND    A 
"  TITANIFEROUS     ANDRADITE    FROM     THE 
NEPHELINE-SYENITE  OF  DUNGANNON, 
HASTINGS     COUNTY,     ONTARIO. 


By  Frank  D.  Adams  and  B.  J.  Harrington, 
Mc  Gtll  College,   Montreal. 


,■1 


'^ 


i 


[P'ROM    THK    AMKRICAN   JoURNAI,   of   ScIKNCR.    Vol..    I,    Maiuii,    ISOfi.l 


ON    A    NEW    ALKALI     HORNBLENDE    AND    A 

TITANIFEROUS     ANDRADITE     FROM     THE 

NEPHELINE-SYENITE  OF  DUNGANNON, 

HASTINGS     COUNTY,     ONTARIO. 


(1 


By  Frank  D.  Auams  and  li.  J.   Harrington, 
Mc  Gil, I,  Cou.KGK,    M()ntrf:al. 


210      Adams  and  Harrington — Alhali  Ilornhlende  and 


Art.  XXII. — 0)i  a  new  Alkali  Hornblende  and  a  titaniferous 
Andradlte  from  the  NephHine-Si/enite  of  Dungannon, 
Hastings  County^  Ontario;  l)y  Frank  D.  Adams  and  B. 
J,  Harrington,  McGill  College,  Montreal. 

In  a  paper  which  appeared  in  the  number  of  this  Journal 
for  July,  1894,  the  discovery  of  a  large  area  of  nepheline- 
syenite  in  the  township  of  Dungannon,  in  the  Province  of 
Ontario,  was  announced  and  the  "geological  relations  and  miu- 
eralogical  characters  of  the  mass  briefly  described. 

One  of  the  many  peculiarities  of  this  rock  is  the  absence 
from  it  of  the  mineral  pyroxene,  which  is  usually  the  chief 
iron-magnesia  constituent  in  rocks  of  this  class,  its  place  being 
taken  by  hornblende  and  mica,  but  even  these  minerals  are 
present  in  comparatively  small  amount.  Of  the  hornblende 
two  varieties,  occurring  in  different  parts  of  the  mass,  were 
distinguished.  Th.^  first,  from  near  the  York  river,  has  a  large 
axial  angle  with  strong  pleochroism  in  tints  varying  from  psile 
yellow  to  deep  green,  and  altliough  containing  a  considerable 
amount  of  soda,  probably  approaches  common  green  hornblende 
in  composition.  The  second  variety,  which  occurs  in  a  series 
of  exposures  about  two  miles  to  the  east  of  the  village  of  Ban- 
croft, is  (piitc  different  in  character,  having  a  small  axial  angle 
with  high  extinction  and  a  much  stronger  pleochi'oism  in  the 
bluish  tints  suggestive  of  arfvedsonite. 

A  number  of  additional  thin  sections  have  been  prepared 
and  in  the  present  paper  the  results  of  a  further  investigation 
of  the  o])tical  properties  and  chemical  composition  of  this 
second  variety  of  hornblende  are  presented. 

Hornhlende — The  mineral  occurs  in  hypidiomorphic  grains, 
which  show  the  usual  hornblende  cleavages ;  it  is  optically 
negative,  a  being  the  acute  bisectrix,  but  the  double  refraction 
is  weak. 

It  possesses,  as  has  been  mentioned,  a  strong  pleochroism  as 
follows : 

a  =  yellowish  green,     b  and  c  =  deep  bluish  green. 

The  absorption  is  c  =  b>  a.  b  and  c,  if  not  quite  equal  in 
absorption,  are  nearly  so,  hence  sections  cut  at  right  angles  to 
the  acute  bisectrix  show  but  little  pleochroism  and  are  nearly 
isotropic,  c  lies  nearest  the  vertical  axis,  but  whether  toward 
the  acute  angle  /9  or  on  the  opposite  side  cannot  be  determined 
as  the  mineral  does  not  possess  a  good  crystalline  form ;  it 
makes  with  the  vertical  axis  a  large  angle  the  extinction 
amounting  to  30°.     The  plane  of  the  optic  axes  is  the  clinopina- 


I 


Titaniferous  Amh'adite  fnmi  Ontario. 


211 


in 
to 


coid,  and  there  is  a  strong  dispersion  —red  greater  than  violet. 
What  drew  especial  attention  to  this  hornhletide  in  the  first 
instance  was  tlie  fact  tliat  it  appeared  to  he  nearly  uniaxial. 
Wiien  a  section,  cut  at  ri^ht  an«i:;les  to  the  acute  hisectrix,  is 
examined  between  crossed  nicols  in  convcrsjfent  li^ht,  a  black 
cross  is  seen  somewhat  thickened  toward  the  intersection  of 
the  arms.  This  cross,  on  revolving  the  stage,  divides  into  two 
hyperbolas,  but  these  separate  from  one  another  but  very  little, 
and  appear  to  separate  less  thnii  they  really  do,  on  account  of 
the  fact  that  the  low  doul)le  refraction  and  deep  color  of 
these  sections  causes  the  hyperbolas  to  be  ill-detined,  while  the 
whole  iield  is  very  dark.  The  dispersion,  however,  makes 
itself  evident  in  the  varying  colors  on  the  sides  of  the  hyper- 
bolas. When,  however,  a  gypsum  plate  giving  a  red  of  the  first 
order  is  inserted  above  the  objective  the  hyperbolas  become  a 
little  better  defined,  altl'.ough  still  not  sufficiently  definite  to 
allow  the  axial  angle  '„o  be  ac(uirately  measured.  The  axial 
angle  is  found  to  be  over  30°,  possibly  as  much  as  45°, 
which,  however,  is  still  very  small  for  hornblende,  being 
about  one-half  the  usual  value.  Our  thanks  are  dne  to  Pro- 
fessor Rosenbusch  for  his  assistance  in  working  out  these 
optical  relations. 

On  examining  a  large  series  of  thin  sections  of  ncpheline- 
syenites  rej)resenting  most  of  the  important  occurrences  hith- 
erto discovered,  only  two  rocks  were  found  which  contain  a 
hornblende  at  all  similar  to  that  above  descril>ed.  The  first  of 
these  is  the  nepheline-syenite  from  the  Cor|)oration  Quarry  at 
Montreal,  in  which  hornblende  with  the  same  small  axial  angle, 
low  double  refraction,  intense  color  and  pleochroism,  large 
extinction  angle  and  high  specific  gravity,  occurs  intergrown 
with  the  augite.  The  second  is  the  hornblende  described  by 
Hackman  under  the  name  of  arfvedsonite  and  which  occurs 
intergrown  with  acgerine  in  the  nepheline-syenite  from  Umptek 
in  the  Kola  peninsula.*  This  mineral,  however,  differs  from 
tyj)ieal  arfvedsonite  in  having  an  extinction  of  about  40°  as 
well  as  in  several  other  iini)ortant  respects.  It  possesses  more- 
over a  very  small  axial  angle,  although  this  fact  is  not  noted 
by  Hackman,  while  in  true  arfvedsonite  the  axial  angle  is 
very  large.  This  Kohv  hornblende  is  much  lighter  in  color 
than  the  hornblende  from  either  of  the  above  mentioned 
Canadian  localities. 

In  order  to  determine  the  chemical  composition  of  this 
somewhat  remarkable  variety  of  hornblende  from  the  Dungan- 
non  I'ock,  it  was  decided  to  separate  a  portion  for  analysis.  A 
considerable  quantity  of  the  rock  was  accordingly  reduced  to 

*  "  Petrosrrapliische  Besclireibimg  fles  Nepheliusyenites  voiu  Umptek,"  von 
Victor  Hackman.     Kuopio,  1894,  p.  14. 


212      AdiUiia  and  Harrington — Alkali  Hornhletuh  and 


powder  and  passed  through  a  fiieve  of  48  incslies  to  tlie  inch — 
the  rocK  beiiij;  rather  coarse  in  ii;rain — and  after  liavinjij  been 
freed  from  dust  was  treated  with  ThouU't's  solution,  Iiavii.g 
a  specific  f^ravity  of  3'18,  in  a  large  separatin<;  funnel.  In  this 
way  an  almost  compU^te  separation  of  the  colored  constituents 
was  effected.  These  latter,  which  sank  in  Tiioulet's  solution, 
were  8ubjecte<l  to  the  action  of  a  bar  maj^net  and  then  treated 
with  dilute  hydrocldoric  acid,  and  various  impurities  thus 
removed.  The  purified  ])ovvder  was  then  treated  first  with 
Klein's  S(jlutic)n,  havin<ij  a  specific  <)^ravity  of  .*»"22,  and  then 
witli  methylene  iodide,  having  a  s|)ecific  <,n*avity  of  3*323.  In 
both  fluids  practically  everythini:;  sank,  only  a  few  composite 
iijrains  floating.  A  microscopic  exasnination  showed  the  pow- 
der now  to  consist  of  grains  of  hornblende  and  o'l  garnet  with 
some  composite  grains  consisting  partly  of  nepheline.  Fur- 
ther separation  became  (h'fficult  since,  as  was  subsefjuently 
ascertained,  the  hornblende  had  a  specific  gravity  of  3433, 
and  the  specific  gravity  of  the  garnet  was  3*730,  wnile  man^ 
eoniposito  grains  consisting  of  garnet  and  ]ie|)heline  had  a 
specific  gravity  practically  identical  with  that  of  the  horn- 
blende. As  the  electro-magnet  was  found  to  be  useless,  both 
minerals  being  readily  attracted  by  it,  Tietger's  silver  nitrate 
method  was  employed.''*  The  silver  nitrate  vv^as  fused  in  a 
properly  arranged  test  tube,  and  after  the  introduction  of  the 
powder,  potassium  niti-ate  in  powder  was  gradually  added  to  the 
fused  mass  until  the  garnet  fell,  the  whole  being  frequently 
stirred  and  maintained  at  a  temperature  of  from  200°  to  2-40° 
C.  On  allowing  the  mass  to  solidify,  a  ])ortion  of  the  powder 
was  found  to  have  collected  at  the  top  of  the  mass,  while  the 
rest  was  at  the  bottom,  the  intervening  jxirt  being  quite  free 
from  mineral  grains.  The  solid  mass  was  then  cut  in  two  and 
the  salts  dissolved  by  treatment  with  water.  After  three  suc- 
cessive se])arations  the  hornblende  w^as  obtained  quite  free 
from  grains  of  garnet — the  onh'  impurities  present  being  some 
composite  grains  consisting  of  garnet  and  nepheline.  This 
powder  was  then  i)laced  under  a  lens  and  all  the  composite 
grains  picked  out  by  means  of  a  fine  needle.  In  this  way  a 
quantity  of  pure  hornblende  sufficient  for  purposes  of  analysis 
was  obtained,  while  the  garnet  was  obtained  directly  in  a  state 
of  purity  without  the  necessity  of  a  firud  separation  by  hand. 

Both  minerals  were  found  to  be  quite  fresh  and  bright  and 
quite  unacted  upon  by  the  fused  salts. 

The  hornblendef  was  then  analyzed  by  Dr.  Harrington  with 
the  following  results: 

*"Ueber  Schwere  Plussipkeiten  zur  Trennung  von  Mineralien."  Neues 
Jahrbuch  fiir  Mineralogie.  etc.,  1889,  ii,  p.  190. 

f  We  would  su>?gest  llastingslte  as  a  varietal  name  for  this  hornblende,  con- 
necting it  with  the  region  where  it  occurs. 


TUitniferoHH  AndradiU  from  Ontario.  213 


Silica 34 

Titaiiiuni  dioxide  ....   1 

Alainiiia   11 

Ferric  oxide 12 

Ferrous  oxide .  - '-'1 

Maiiganou8  oxide 

Lime 9 

Majifnesia 1 

Potasli 2 

Soda 3 

Water* 


184 
'527 
■517 
021 


•62 !» 
•807 
•353 
•286 
•290 
■348 


Specific  gravity 


9n-0()l 
3-433 


The  atomic  and  qrantivaleiit  ratios  dediicible  from  the  above 
analysis  are  as  follows: 

Atomic. 
570X4  =  2280 


Si. 
Ti 

Al 


19X4  = 

226X-'^  = 


Fe'" 158X3: 

Fe" 305x2: 


Mn 
Ca. 

Mg 
K.. 

Na 


9X2  = 
176X2  = 

34X2  = 

48 
106 


76 
078 
474 
610 

18 
352 

68 

48 
106 


Quantivalent. 
2356      2356 


j.  1152^1 

1 


I 

^2354 


The  ratio  of  (R,0  +  RO)  :  K./),  :  SiO,  is  601  :  192  :  589,  or 

approximately  3:1:3,  and    obviously    the  mineral  is  a  true 

I     II     III 
orthosilicate  agreelni;  fairly  with  the  formula  (R3U)3  R^SijO,,, 
or,  more  fully,  (Fe,  Mn,  Ca,  Mjj:,  K,,  Xa,),  (Fe,  Al),  (Si,  Ti),  O., 
— a  constitution  analofirous  to  that  of  i^arnet. 

So  fi'r  as  we  are  aware  no  other  hornblende  containmg  so 
small  a  proportion  of  silica  has  been  analyzed  ;  but  the  small 
percentage  of  silica  is  explained  by  the  large  proportions  of 
ferrous  and  ferric  oxides.  This  is  made  plain  by  the  following 
formulae  and  the  corresponding  percentages  of  silica  deduced 
from  them : 


Formula. 
3FeO,  Fe.O,,  3SiO, 
3Ca(),  Fe^O,,  3SiO, 
3FeO,  AI.P3,  3SiO, 
3Na,0,  Ai„0,,  3SiO, 
3CaO,  Ai;03,  3SiO, 


C.  of  SiOa. 

32-19 

35-43 

30-14 

38-38 

40-00 


*  Loss  after  igniting  for  about  llfteen  minutes.     On  furtlier  ignition  the  powder 
gained  in  weight  owing  to  oxidation  of  tlie  ferrous  oxide. 


214      Adams  and  Jl<irrhnji<m — AllaVi  Ifoi-nhbride  and 

The  Diiii^aniKHi  liornhUMide  i«  iiitcrestintif  iti  oomiocitioii  witli 
the  viovvs  of  Scliiirizcr,  wh(»  sii<i;<(e.ste(l  in  isS4*  that  many  of 
the  uhiininons    horn'ikuidcs  ii»i<;ht  he   regarded  as   molecular 

compounds  of  the    m(3tasilicate  actinolite,  Ca  (M^,Fe),  Hi«0,„ 

I    If     III 
and    tlio  orthosilicate  (U,jIl),U.,Si.,()„,   for  which  ho  employed 

the  name  Hynta<^matite,  orij^inally  ^iven  hy  Hreithaupt  to  a 
hlack  hoi'nl)lendo  froin  VcHUviu.s.  The  honihlonde  from  th') 
Island  of  .Ian  Mayen,  analyzed  hy  Scharizer,t  and  that  from 
Bohemia,  iitialy/ed  hy  Schmidt,:};  ai^rc^e  closely  with  the  so-called 
"  syntagmatite  molecule."  The  8ten/-elher^  mineral,  analyzed 
hy  Uammelsberg,^  also  approximates  to  it;  hut  these  three  and 
the  Duni^annon  hornhlende  are  the  only  ones  yet  examined,  so 
far  as  we  are  awan;,  that  <!^ive  at  all  closely  the  syntagmatite 
ratios.  The  followini>-  tal)le  gives  the  analyses  of  these  four 
minerals  and  the  molecular  ratios  deducihle  froin  them  : 


• 

Stet)/,cl 

Dimgaii 

Jau  Mayeu. 

Molec.  R. 

Bohemia.  Mol.  11.    berg. 

i 

Mol.  U.          QOQ. 

1 

Mol.  R. 

RiO,     39167 
TiO,      .... 

653 

653 

39-66 

0-89 

661 
11 

39-62 
►  672    „.,,) 

660  )   „,.„  34-184 
2  \  *^"2    1-527 

™J-CS, 

AliiO,  14-370 
Fe,Oa  12-423 

140 

78 

•  218 

14-83 
12-37 

145 

77 

2,„  H-f»2 

146?   210 '^■•^'' 
04  f  ^'"  12-621 

■i^fm 

FoO        5-856 

811 

1-97 

27] 

767 

106] 

21-979 

305 1 

MnO       1-505 

21 

.. 

0-24 

3 

0-629 

9 

MgO    10-521 

263 

14-23 

356 

11-32 

283 

1-353 

34 

\ 

CaO      11-183 

200 

\-  648 

12-74 

227 

\-  663  12  65 

226 

j.  685    9-867 

176  )■  620 

KaO       2-013 

21 

1-25 

13 

2-18 

23 

2-286 

24 

NuaO     2-478 

40 

2-47 

40 

112 

18 

3-290 

53 

HaO         -396 

22J 



--. 

0-48 

26  J 

0-348 

19J 

99-912 

100-43 

il0067 

99  601 

In  all  four  analyses  the  ratios  for  (R,/)  +  RO)  :  11,0,  :  SiO, 
(including  TiO^  when  present)  are  practically  3:1  :  8,  or,  to 
give  the  exact  figures  (excluding  water): 

(RoO  +  RO)  :     R^C 

Jan  Mayen -2-87       : 

Bohemia.    2-99       : 

Stenzelberg 3-1 4       : 

Dungannon 3-l'2       : 

The  ratio  (R,0-f-CaO)  :  (Mg,  Mn,  Fe)0  is,  as  observed  by 
Scharizer  in  the  case  of  the  Jan  Mayen  and  IJohemian  horn- 
blendes, approximately  3  :  4,  thus : 


Oa 

: 

SiOa 

I 

2-99 

1 

3-02 

1 

3-15 

1 

3-07 

*N.  .lahrb.  f.  Mia.,  1884,  ii,  p.  143. 

f  loc.  cit. 

X  Min.  Mitlh,  iv,  23,  1831. 

g  Pogg.  Ann.,  1858,  ciii,  454. 


\- 


192 


Tttaniferoim  AntJrndiiefrom  Ontario.  215 

Includiiig  Water.  KxeludiD«  Water. 

(R,0  +  CuO)  :  (Mk,  Mn,  Ke)().  (R.,0  +  CaO) :  (Mfir,  Mo,  Fe)0. 

Jan  Mayen 3       :  387  3     :     4-17 

Bohemia 3       :  4-10  3     :     4-10 

Stcn/A'lberg 3        ;  4-02  3     :     438 

Diuiganiion 3       ;  3-84  3     :     411 

Scluirizer  adopts  the  fore<;oiTig  ratios  (3  :  1  I  -5  and  8  ',  4)  as 
those  of  syntagmatite  in  calcnhitin<i;  the  comno.Hition  of   horn- 

I       II  Ml 

blendes  intermediate  between  (Fiji),  li,Si/),,  and  actinolite. 
lie  assumes  in  tlie  first  place  that  all  the  alumina  and  ferric 
oxide  belonfi^  to  the  synta<?matite  molccide  (i).  The  sum  of 
the  AI3O3  and  Fe./),  molecules  (from  the  molecular  ratio)  mul- 
tipled  I)y  three,  ^ives  (Si(),)i;  on  the  one  hand  and  (lv,j()  + 
RO)s  on  the  other.  The  sum  of  (K,0  +  liO)i;  divided  in  the 
proportion  of  3:4  gives  (R,0  +  Ca())i"  and  :^^<r04-FeO)i;. 
Subtractinfjj  (MgO  +  FeC))i;  from  the  sum  of  the  correspundin 
ra6leculcs  deduced  from  the  analysis  gives  (MgO-fFe())A — that 
18  the  number  of  molecules  of  magnesia  and  ferrous  oxide 
belonging  to  tho  actinolite  molecule  (A) — and  (Mg()4-FeO)A 
divided  by  three  (see  actinolite  foi-mula)  gives  the  lime  mole- 
cules of  the  actinolite  (CaO).v.  This  value  subtracted  from 
the  total  nund)er  of  lime  molecules  gives  ((^aO)i;,  and  (CaO)s 
subtracted  from  (ri,0  +  CaO)i;  gives  the  alkali  molecules  (in 
some  cases  inc' iding  II^O).  Finally  (MgO-f-CaO)^  gives 
(Si03}A.  These  statements  will  be  made  clearer  by  the  follow- 
ing example,  one  of  those  selected  by  Scharizer. 

Hornblende  from  Edentille,  analyzkd  by  Ramjielkuero. 


Molee.  R. 

Original 

Original 

deduced 

yyntag- 

Calculated 

analysis 

■    analysis. 

from 
analysis. 

861 

matite. 

Actinolite. 

comi)osition. 

calc.  to 
100. 

SiO, 61-67 

222 

609 

51-97 

52-66 

Al,03   ..      5-75 
Fe„0,  ..      2-86 

56 

18 

18  f  '* 



5-99 
3-00 

5-86 
2-91 

MgO...    23-37 

584 

127^ 

457 

24-35 

23-82 

CaO    ...    12-42 

222 

70 

152 

12-96 

12-66 

Na,0...     0-75 

12 

12  ).222 
9 

.    . 

0-78 

0-78 

K,0 0-84 

9 

0-88 

9-86 

H.O 0-46 

25 

4 



0-07 
10000 

0-47 

98-12 

■    ■               _ 

100-00 

216      Adams  aiid  Harrington — Alkali  Hornblende  and 

Here  (SiOJs  =  3(56  + 18)  =  222 

(R,0  +  R0)S  =  3(56  +  18)  =  222 

(MgO).=4<M+^),=^=127 
(MgO)A  =  584-(MgO)2  =  584-127  =  457 

3  3 

(CaO)2  =  222  — (CaO)A  =  222-152  =  70 
(Na,O  +  K,O  +  H,O)i;=(R,O  +  CaO)2-(CaO)s  =  96-70=25 
But  (Na^O  +  K.O)!  =  12  +  9  =  21 

.•.(11,0)2=4 
Finally  (SIOJa  =  (MgO  +  CaO)  a=  457  +  152  =  609 

_  Having  thus  deduced  the  molecular  ratios  of  the  syntagma- 
tite  and  actinolite,  tlie  numbers  for  each  constituent  are  multi- 
plied by  the  corresponding  molecular  weights,  in  order  to 
obtain  the  theoretical  relative  weights  of  the  constituents  of 
the  mixed  hornblende. 


Syntagmatite. 
222X60   =  13320 
56X102-6=  5745 
18X160  : 


127X  40 

70X  56 

12X  62 

9X  94 

4X  18 


2880 

5080 

3920 

744 

846 


32607 


Actinolite. 
609X60  =36540 


457X40  =  18280 
152X56=  8512 


63332 


Then, 

(32607 +  63332):  (13320  + 36540)  ::l00:a; 

and  a?  =  51*97  =  p.  c.  of  SiO,  in  the  mixed  hornblende.  And 
in  like  manner  the  percentages  of  the  other  constituents  are 
calculated. 

But   32607  :  63332   practically  as  1:2,  and  therefore    the 
formula  of  the  Edenville  hornblende  might  be  regarded  as 

RJi,Si30^,  +  2(Mg3CaSi,0,,) 

or  as  Scharizer  gives  it 
II  III 
10(»i,H.Si,OJ  +  20(Mg,CaSi,OJ  _.._  . 


Titaniferous  Andradite from  Ontario.  217 

The  analyses  selected  by  Selmr'zer  agree  remarkably  well 
with  his  theory,  but  there  are  aluminous  hornblendes  whose 
consti  ution  cannot  be  readily  explained  n  tins  way  and  which 
at  the  same  time  cannot  be  referred  to  the  pargasite  orthosili- 

Garnet  —In  the  hand  specimens  the  garnet  is  seen  to  possess  a 
deep  reddish-brown  color.     In  the  thin  sections  it  is  a  paler 
brown  although  still  deeply  colored.    It  is  not  found  in  all  parts 
of  the  mass  and  where  it  does  occur  is  usually  present  only  in 
small  amount.     It  possesses  the  usual  high  index  of  retraction 
and  is  quite  isotropic,  occurring  usually  In   irregular   shaped 
erains  but  in  some  few  cases  showing  distinct  crystalline  torm. 
It  frequently  holds  a  few  large  inclusions  which  usually  con- 
sist of  calcite  in  single  individuals,  although  the  garnet  is  per- 
fectly fresh  and   the  calcite  shows  no  distinct  evidence  ot  a 
secondary  origin.    It  moreover  sometimes  holds  inclusions  ot  the 
hornblende  above  described,  oi  pyrite,  iron  ore  and  even  ot 
nepheline.     A  garnet  resembling  this  occurs  in  small  amount 
associated   with  a  similar  hornblende,  as  above  mentioned,  in 
the  nephelinesyenite  of  the  Corporation  Quarry  at  Montreal, 
and  it  also  contains  as  inclusions  most  of  the  other  constituents 
of  the  rock.     The  same  is  also  true  of  the  melamte  in  the 
nepheUne-syenite  of  Alno.f  ...    ,  ,  i  i.:^„„ 

Before  analysis  the  garnet  was  purified  by  several  separations 
with  fused  silver  nitnite  and  on  careful  examination  with  the 
microscope  the  grains  appeared  to  be  entirely  free  t';o>n  foreign 
matter.  With  the  pycnometer  their  specific  gravity  at  lb  _0. 
was  found  to  be  3-739.  Chemical  analysis  gave  the  following 
results  : 

Silica -----    =^6-H04 

Titanium  dioxide ^  !!l^ 

•       Alumina..- ^  oop 

Fei-ric  oxide 15-996 

ferrous  oxide 3-852 

Manganous  oxide 1-301 

Lim" 29-m 

Magnesia.. 1  3b4 

Loss  on  ignition - '^^^ 

-"  99-57Y     . 


The  atomic  and  cpiantivalent  ratios  deduced  from  the  above 
analysis  are  as  follows : 

♦SeeScharizer's  paper,  loc.  cit.,  p.  156.  ••-.„„„   a    n   Hncbom 

f  "  Ueber  das  Noplielinsyenitgebiet  auf  der  Insel  Alao,    von  A.  G.  Hogbom. 
Geol.  FiJren.  i.  Stockholm  Forb.,  1895,  p.  U4. 


218     Adams  and  llarvin(jton — Alkali  Hornblende,  etc. 


1176 


Atomic. 

Si 610X4  =  2440 

Ti iaX4=       52 

Al    192X3  =     576 

Fe"' 200  X  3  =    600 

Fe" 5-^,X2  =     106  ^ 

Mn .-      18X2  =       36    I 

Ca 523X2  =  1046    J>i290 

Ms; 35X2=       70    I 

32  J 


Qiiantivalent. 
I  2492     2492 

] 


^2466 


II 


32 


The  ratio  for  RO  :  R,0,  :  (SiTi)O,  is  OSl)  :  IIMI  :  623,  or, 
calculating  the  titanimn  as  Ti,0„  629  :  203  :  610  =  3:1:3. 

The  analysis   therefore  accords  well  with  the  ordinary  garnet 

II  III 

formula  3Tl(),  R^O,,  3810,  or  RgR^SijO,,,  and  the  mineral  may 
be  regarded  as  a  ti^aniferous  andradite,  with  a  consideral)le 
proportion  of  the  ferric  oxide  replaced  by  alumina.  In  com- 
position it  resembles  somewhat  the  brown  garnet  from  the 
Island  of  Stoko,  analyzed  by  Lindstrom.^ 

By  way  of  comparison  the  analysis  of  the  Stoko  garnet  and 
also  one  of  a  garnet  from  the  nepheline-syenite  of  the  Island 
of  Alnof  are  included  in  the  following  table. 


Stoko.        Molec.  R. 


SiOa 2G-63 

TiOa 

AlaOa  ...     997 
FeaO,  ...   13-45 

FeO 2-28 

MnO -63 

CaO 35-90 

MgO -28 

Na»0 

Ign -16 

99-30 


610      610 


98  ) 
84  f 

32^ 

9  I 

641  ( 

^  r 
...  I 

9J 


182 


698 


Aliio.     Molec.  R.        Dungannon.     Molec.  R. 


31-15 
6-73 

3-14 
23  83 

'-58 
33-44 

•68 


99-55 


G03 


180 


597  V  616 


36-604 
1-078 

9-771 
15-996 

3-852 

1-301 

29-306 

1-384 

•285 
99-577 


*Zeitschr.  fur  KryHt.  u.  Mm.,  xvi,  ICO.  1890. 

f  Sahlboin,  ia  tlie  paper  by  Ilogboin  already  cited. 


610  ) 

13  f 

96  I 
100  J 

I  63 

18 

523 

I  35 

16 


623 


196 


)■  645 


